Examples of the said refuse incineration products, whose processing can be carried out by the method according to the invention, are grate throw-off, siftings, grate slag, fly dust, filter dust, residue from flue gas purification and/or analogous residues from refuse incineration.
In this connection, it is pointed out that, as used in this specification, the word "refuse" has the same meaning as the word "waste" which is commonly used in some areas in place of the word "refuse".
Examples of the said analogues, whose processing can be carried out by the method according to the invention, are slags, ashes, dusts, contaminated materials, spent catalysts, used glass, foundry sands, scrap metals and the like, whose chemical composition and properties are similar to those of refuse incineration products with respect to their hazard potential for the environment.
A process of the type described at the outset is known from the article by F. J. M. Lamers et al. "Production and Application of a Useful Slag from Inorganic Waste Products with a Smelting Process", which was published in "Waste Materials in Construction" (Proceedings of the International Conference on Environmental Implications of Construction with Waste Materials, Maastricht, Netherlands, 10th-14th Nov. 1991, edited by Goumans, van der Sloot and Aalbers).
This method is, however, applicable only to fly ash. To produce a slag having useful pozzolana reaction properties or hydraulic reaction properties, it is necessary to add limestone and, if appropriate, alumina or another alumina-containing compound, because the fly ash contains too high a proportion of silica and/or silicates for the production of the desired reaction properties. On the other hand, fly ash does not cause a particular problem which occurs with relatively heavy refuse incineration products such as, for example, grate throw-off and siftings, namely that such refuse incineration products still contain considerable quantities (for example up to 5% by weight) of organic waste materials which have been incinerated only partly or not at all. Thus, this method known from the article by Lamers only incompletely solves the problem of the disposal of refuse incineration products.
With a view to complete combustion of the refuse incineration products, the oxidation of molten metallurgical waste products by blowing oxygen-containing gas into the melt through a lance, as is known, for example, from WO-91/02824, can be considered. In this method, however, reducing conditions always apply in the melt, with the exception of the surroundings of the lance. This method fulfills the purpose of causing volatile elements and their compounds to escape in a gas phase and then precipitating and/or washing them out of the latter, but other elements and their compounds are collected in the slag and render the latter toxic or at least in acceptable within the scope of the regulations which will be discussed below.
The disposal of refuse incineration products and/or analogues causes extreme concern in all industrial countries. The refuse incineration products can generate toxic gases and eluates, and the products from the incineration of hazardous waste are certainly toxic. While an increasing volume of toxic products arises, it becomes increasingly difficult to store the rising volume of toxic products in suitable landfills. The problem arises above all in the disposal of highly toxic substances containing sulphur compounds and/or halogen compounds.
In a typical refuse incineration plant of an average-sized town such as Zurich, about 300,000 to 400,000 tons of refuse have to be incinerated per year, about 350 kg of refuse incineration products being produced from 1,000 kg of refuse, and these comprise in turn about 300 kg of grate throw-off, about 40 kg of filter dusts and about 10 kg of products from the more elaborate flue gas purification. Hitherto, this slag has been freed of scrap and coarse organic substances as well as possible by simple mechanical means and, if appropriate after fractionation and/or stabilization with cement, used in road construction. However, more refuse incineration products arise than can be disposed of in road construction. Apart from this, the said manner of disposal of the refuse incineration products is not without concerns regarding pollution of tile environment.
The recent Swiss "Technical Wastes Regulations" in principle preclude the use of refuse incineration residues as building material, exceptions for construction purposes are permitted only with restrictions in connection with the construction of roads, squares and dams, and this use of the refuse incineration residues must be recorded in a kind of contaminated materials registry.
Refuse incineration residues which can be used as building material must in this case be of a so-called earth crust quality or rock quality, wherein the environmental pollution is substantially below that defined by the "Technical Wastes Regulations".
The detoxification of tile output of refuse incineration plants (refuse incineration products in tile form of solids and gases) has already been the subject of various proposals.
From DE-C-3,608,005, it is known, for the disposal of hazardous waste which contains toxic or environmentally harmful constituents or causes these to be formed in pyrolysis or incineration, first to pyrolyze the refuse at 500.degree.-900.degree. C. The gases thus generated are then passed together with an oxidizing agent such as air or steam through a melt, held at 1400.degree.-1600.degree. C., of iron or steel, copper, metal oxide or salt. Nickel, copper and arsenic dissolve in the iron melt as elements or compounds, and manganese and chromium collect in the oxidized form in the slag melt. Heavy metals which have a high vapor pressure at the melt temperature, for example lead, tin, zinc, cadmium and mercury, and also sulphur compounds and/or halogen compounds, escape with the gases which are then purified in such a way that, in addition to inert gases, they mainly contain hydrogen and carbon monoxide and can be used as fuel. As a result, the entire process can be operated largely without energy being supplied. The remaining toxic constituents are firmly fixed in the slag, so that these can be put into landfills without more stringent safety requirements, but nevertheless only in landfills, whereas a different use of the slag cannot be considered because of its toxic constituents. In this known method, however, the gases from the pyrolysis of the hazardous waste are subjected to a treatment, whereas no treatment of toxic slag from a conventional refuse incineration plant is proposed.
From EP-C-175,207, it is known, for the disposal of carbon-containing or organic hazardous waste, to introduce this into a hot fluid such as an iron-containing metal melt at a temperature of over 1000.degree. C. and to add an oxidation gas in order to oxidize the refuse in the hot melt. After they have been detoxified, the gases generated contain, in addition to inert gases, mainly hydrogen and carbon monoxide. This known method is aimed at the complete destruction of hazardous organic substances such as dioxin, whereas no indication is given with regard to the elimination of metal or slag, which contain toxic constituents. From this method, it is known to contact the refuse with an iron melt, but in this known method it is the hazardous waste itself which is subjected directly to a treatment, whereas no treatment of toxic slag from a conventional refuse incineration plant is proposed.
From JP-A-54-78,866, it is known, for the disposal of hazardous waste, to introduce this into the slag of a converter and to add pulverized coal or spent oil and also an oxidation gas, in order to oxidize the refuse in the hot melt and to absorb the remaining ash in the slag melt. The gases generated contain, in addition to inert gases, mainly hydrogen and carbon monoxide. The slag melt is kept under reducing conditions, so that iron, calcium and phosphorus are removed from the slag and are precipitated below the latter as an alloy melt. This alloy melt is separated into an iron-containing fraction and a fraction which contains oxides of calcium and phosphorus. The iron-containing fraction can be used in steel manufacture and the calcium-phosphate-containing fraction can be used as fertilizer, while the slag is recycled. This known method is also directed to the complete destruction of hazardous organic substances, whereas no indication is given with regard to the elimination of metal or slag, which contain toxic constituents. From this method, it is known to contact the refuse with an iron melt, but in this known method it is the hazardous waste itself which is subjected directly to a treatment, whereas no treatment of toxic slag from a conventional refuse incineration plant is proposed.
From EP-C-162,215, it is known to use slag from the refuse incineration together with clinker in the manufacture of cement. The refuse is incinerated in hot exit air from the cooling of the cement clinker. In the hot gases thus generated at 1000.degree.-1400.degree. C., the raw cement meal is calcined, a part of these gases being taken off at the inlet of the clinker rotary kiln, in order to condense and to remove the volatile heavy metals therefrom. The slag from the refuse incineration is quenched in water; it has latent hydraulic properties and can be admixed to the cement. However, it is not ensured in this method that all toxic constituents have been removed from the slag, so that this slag may not be admixed to the cement without further measures in any desired application. In this known method, the slag from a conventional refuse incineration plant is thus further processed without regard for its compatibility with the environment, but no treatment of toxic slag from a conventional refuse incineration plant is proposed.
From BE-A-868,430, it is known to reduce basic slag from the oxygen treatment of cast iron to Portland cement. Alumina and silica are added to the slag melt and the atmosphere is made highly reducing, in order to reduce iron oxide and manganese oxide in the slag and to separate out a manganese-containing iron melt below the slag melt. After the reduction, lime is added to the slag in order to adjust the composition of the slag melt to that of Portland cement. Even in this method, however, it is not ensured that all toxic constituents have been removed from the slag, so that this slag may not be admixed to the cement without further measures in any desired application. With this known method, no treatment of toxic slag from a conventional refuse incineration plant is thus proposed.
Viewed as a whole, it is the object of the known methods mentioned above to produce refuse incineration residues which are in the form of granulated glass, which is resistant to leaching, and are then put into a landfill.
A method for processing refuse incineration products, which are in the form of solids, to give products which are environmentally acceptable and can be used without reservations for building purposes and which are of earth crust quality or rock quality, as is strictly defined in the "Technical Wastes Regulations", is thus not yet known.